In automotive engines, crankshaft rotation is transmitted to a cam shaft via a timing chain (hereinafter simply called chain), and valves in combustion chambers are opened/closed as the cam shaft rotates.
Often, driving of the cam shaft as described above is achieved by a transmission apparatus or chain drive apparatus, which includes a drive sprocket attached to a crankshaft; a driven sprocket attached to the cam shaft; a chain wound around the drive sprocket and the driven sprocket; and a pivotable chain guide disposed on a slack side of the chain; a chain tensioner which presses the chain guide toward the chain; and a fixed chain guide disposed on a tension side of the chain.
In this arrangement, the pivoting chain guide presses the chain with the chain tensioner's urging force, thereby keeping the chain under a constant tension whereas the fixed chain guide reduces chain vibration while keeping an ideal chain tracking line.
The pivoting chain guide and the fixed chain guide used in such a chain drive apparatus as described above are typically of a sliding type, having a guide surface extending in a chain tracking direction for making sliding contact with the chain. A problem with this type of chain guides is a large transmission loss of torque due to a large tracking resistance of the chain since the contact with the chain is sliding contact.
In an attempt to solve such a problem as this, there are proposed chain guides (Patent Literature 1 through 3) each including a guide base extending in a chain tracking direction; a plurality of roller shafts attached to the guide base at an interval along the chain tracking direction; and rollers each supported rotatably by one of the roller shafts. In these chain guides, each roller has a cylindrical outer circumferential surface for guiding the chain.
These chain guides make use of rolling contact with the chain and therefore, the chain has a smaller tracking resistance, which results in an advantage of smaller transmission loss of the torque.